This disclosure relates to a method for regulating the surface temperature of a glow plug by closed-loop control. One known method for regulating surface temperature of a glow plug is disclosed in DE 10 2012 105 376 A1.
In such methods, a target resistance is determined from a target temperature by means of a resistance temperature characteristic of the glow plug, and the actual resistance of the glow plug is then regulated to the target resistance by closed-loop control. By means of a resistance temperature characteristic, a target value of the electrical resistance is associated with a target value of the temperature and the supply of electrical power to the glow plug is regulated so that the electrical resistance and the temperature associated with it are brought into conformity with the target value of the electrical resistance or with the target value of the temperature. The quality of the temperature regulation is limited by the accuracy of the resistance temperature characteristic. It is therefore important to know the resistance temperature characteristic of the glow plug used as precisely as possible.
One option for determining the resistance temperature characteristic of a glow plug is to keep the motor at standstill for a few minutes and then to heat the glow plug for a certain time, e.g., for about one minute, with a constant predetermined electric power until the glow plug reaches an equilibrium state, the temperature of which is defined by the heating power and heat dissipation with the motor at standstill and is therefore known or can be determined by appropriate measurements for all future cases.
In practice, it has been found that when regulating the surface temperature of a glow plug, even when using a precisely determined resistance temperature characteristic, considerable control deviations can occur, which can easily amount to 50 K.